Featured Review Cellscience Reviews Vol 4 No 2 ISSN 1742-8130

The Cellular Mechanisms of Learning and Memory:
Pattern Separation and Pattern Completion In the Hippocampal Formation

In the neurosciences, learning and memory remains a primary focus of studies at many different levels of analyses, with efforts focused largely on the molecular and cellular correlates of the activity-dependent synaptic changes, such as long-term potentiation (LTP). However, a coherent picture of how LTP is used by brain structures such as the hippocampus to allow the storage of information (learning, or encoding) and rapid and relatively accurate recollection (memory or retrieval) has been lacking. Here, an 'information-theoretic' view is presented of how the brain learns and retains learning over time. Using a physiological and dynamical view of hippocampal operations, pattern separation and pattern completion are suggested as the physiologic mechanisms mediating learning and memory, respectively. In this view, memory is a function of pattern completion in the CA3 network and reactivation of the neocortex, whereas learning involves enhanced dentate-CA3 output, pattern separation, and sparse encoding within the CA3 region. Novelty detection is suggested to signal the hippocampus and dentate to switch from a 'state' of pattern completion and retrieval to one of pattern separation and encoding.

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